The post-mortem distributions and concentrations of calcium, silicon, and aluminum in plaques from brains of patients with Alzheimer's disease have been determined from elemental images and spectra acquired by wavelength-dispersive x-ray spectroscopy on a computer-controlled Cameca MBX electron beam x-ray microanalyzer. Both air dried and freeze-dried cryo-sections 8-10 micrometers thick from fresh frozen specimens with no chemical preparation were analyzed. In air-dried sections the concentrations of silicon and aluminum in the plaques were found to be similar to matrix control levels; the concentration of calcium was about fifty per cent higher in the plaques. In freeze-dried sections the concentration of silicon was the same in matrix and most plaques; the concentrations of calcium and aluminum in plaques were found to be up to ten times matrix levels. These results differ from those obtained by other workers using fixed material or purified cores. The implications are that chemical preparation significantly alters the elemental distributions in the sections.